This invention relates to a control method for vehicles and, more particularly, to a clutch and engine control method.
An automatic clutch known in the art automatically controls a friction clutch of an automobile, e.g., a dry-type, single disk clutch, by means of an electronic control apparatus. Specifically, the known automatic clutch automates the transmission and disengagement of motive power by a friction clutch by means of an electronic control apparatus which controls an actuator that operates in response to hydraulic, pneumatic or negative pressure. A control apparatus for an automatic clutch of this type is disclosed in the specification of Japanese Patent Publication No. 50-12648, wherein the engaged state of a clutch is gradually varied depending upon an increase in engine rpm, and in the specification of Japanese Patent Application Laid-Open No. 52-5117, wherein the rate at which a clutch is engaged is varied in accordance with engine rpm.
In a vehicle equipped with such an automatic clutch, operation is no different from that of a vehicle having an automatic transmission equipped with a torque converter. To propel the vehicle, therefore, the driver depresses the accelerator pedal a considerable amount and continues to hold the pedal depressed until a certain velocity is attained. More specifically, with an automatic transmission having a torque converter, the engine is constantly subjected to a load of a certain magnitude in the drive range. No matter how far the accelerator pedal is depressed, the engine will not "race" excessively. In addition, the higher the engine rpm and the greater the slip factor, the greater the torque ratio obtained. This increases the drive torque as well as the engine braking torque, thereby suppressing racing.
In a vehicle equipped with the above-described automatic clutch, however, the clutch engaging operation is performed after the rise in engine rpm, thereby resulting in the following inconveniences. First of all, when the clutch starts to be engaged, engine rpm rises considerably, during which time the vehicle itself is completely at rest. Therefore, (1) the engine races, (2) the amount of clutch slip sustained in a half-clutch operation becomes large owing to engine racing, thereby resulting in clutch wear and reduced clutch useful life, and (3) fuel consumption rises as a result of (1) and (2). Secondly, after the driver depresses the accelerator pedal, a certain period of time is required before engine rpm rises. Since the clutch is controlled in accordance with the rise in engine rpm, starting response diminishes markedly. Furthermore, since the vehicle will not move forward under these conditions even when the accelerator pedal is depressed, the driver tends to step down on the pedal excessively. This not only aggravates the phenomena (1) through (3) but also increases the risk of sudden forward movement since the accelerator pedal will be in a considerably depressed state and the engine rpm high when the vehicle starts moving. In particular, problems are encountered when attempting to move the vehicle a slight amount at low speed, as when parking an automobile in a garage or close to a curb.
In the conventional clutch control system, a proportional constant is set so that the clutch engaging operation takes place comparatively slowly in order to realize a smooth start and minimize both sudden forward movement and shock when movement starts. As a result of setting the proportional constant, clutch control is performed slowly at gear shifting following the start of the vehicle, thereby lengthening the time for shifting and making it difficult to achieve smooth acceleration after the gear change. In addition, shock is produced when engine rpm experiences a sudden change. When a proportional constant suitable for shifting is set, on the other hand, problems in control are encountered when starting the vehicle from rest.
As regards engine fuel supply means, e.g, a throttle valve in a gasoline engine or a fuel injection pump in a diesel engine, certain problems are encountered because such means are controlled independently of the clutch. Specifically, where the accelerator pedal is depressed to accelerate the vehicle from a state in which the clutch is disengaged when the vehicle is started or travelling at low speed, the clutch is controlled comparatively slowly to avoid shock and realize smooth acceleration, as set forth above. As shown in FIG. 8, herein which is a graph showing degree of clutch engagement plotted against time, clutch engagement starts at time t.sub.o and rises to 100% (full clutch engagement) at time t.sub.l. A so-called "half-clutch" state prevails between times t.sub.o and t.sub.l. On the other hand, in, say, a gasoline engine, a throttle valve for controlling the amount of fuel and air supplied to the engine has its opening controlled, independently of the clutch, in accordance with the amount of accelerator pedal depression to increase the fuel and air supply and raise the engine rpm.
Until the clutch becomes fully engaged, therefore, the engine races and the driver experiences an unpleasant sensation. At the same time, the engine rpm and the vehicle speed are not linearly related (1:1) until the clutch is fully engaged. This makes it very difficult for the driver to operate the accelerator as when starting the vehicle from rest. In addition, since the clutch is caused to slip while the engine is rotating at high speed, drawbacks are encountered in terms of fuel consumption and clutch wear.